1. Field of the Invention
The present invention is directed toward an apparatus and formulation for photodynamic therapy. More specifically, the invention is directed toward photodynamic therapies that include the use of controlled heat, local anesthetic-photosensitizer combined formulation, pH manipulation, and/or the solidification of the formulation after application.
2. Background
Photodynamic therapy uses photosensitizers activated by light to induce cell death via the formation of single oxygen or other free radicals. Photodynamic therapy is increasingly used to treat skin cancer, psoriasis, and other skin disorders. In a typical treatment, a formulation containing a photosensitizer is applied on the skin or other tissue to deliver the photosensitizer into the tissues by permeation. Light of proper wavelengths is then applied onto the treated tissue. The photosensitizers in the tissue cells are broken by the light to release single oxygen or other free radicals which kill the tissue cells. One commonly used photosensitizer is delta-aminolevulinic acid (ALA). It is desirable to deliver a local anesthetic agent to a patient's skin when the patient is undergoing a procedure using a photosensitizer. This can reduce or eliminate the pain caused by the single oxygen or other free radicals produced by the light treatment. In some cases, the anesthetic is administered after the delivery of the photosensitizer and before the light treatment requiring an additional procedure and/or additional waiting time.
There are several problems associated with the current photodynamic therapy methods and formulations involving ALA or its derivatives (such as methyl, ethyl or propyl esters): 1) It takes at least 4-6 hours of contact time to deliver sufficient amount of ALA into the tissues 2) the penetration of ALA into the treated tissues sometimes is not deep enough, 3) single oxygen or free radicals released by the light in the tissues causes pain, and 4) in some of the currently used formulations (2) of ALA are chemically unstable.